Any idea.

Try to save file to a server across a VPN line. It intermittenly can be
saved and some time comes up with writing error. Looking into the
destination folder, some temp file are created. E.g. save an image file
named inform.jpeg, when it failed to save successfully, temporary file name
like SAV01.tmp was created.

Don't know how to address / get a solution to this problem. Is this a VPN
line problem or some other reasons causing that?

This workstation runs nwc 4.91sp4. server runs netware 6.5 sp5
slp DA is up with no slp error logged.